[RFC,v2,1/6] sched: Unify runtime accounting across classes

diff --git a/include/linux/sched.h b/include/linux/sched.h
index a6bf77c346876..f7b9ba04970bc 100644
--- a/include/linux/sched.h
+++ b/include/linux/sched.h
@@ -424,7 +424,7 @@  struct sched_statistics {
 
 	u64				block_start;
 	u64				block_max;
-	u64				exec_max;
+	s64				exec_max;
 	u64				slice_max;
 
 	u64				nr_migrations_cold;
diff --git a/kernel/sched/deadline.c b/kernel/sched/deadline.c
index 3862a28cd05d0..2ece83b5991f5 100644
--- a/kernel/sched/deadline.c
+++ b/kernel/sched/deadline.c
@@ -1221,9 +1221,8 @@  static void update_curr_dl(struct rq *rq)
 {
 	struct task_struct *curr = rq->curr;
 	struct sched_dl_entity *dl_se = &curr->dl;
-	u64 delta_exec, scaled_delta_exec;
+	s64 delta_exec, scaled_delta_exec;
 	int cpu = cpu_of(rq);
-	u64 now;
 
 	if (!dl_task(curr) || !on_dl_rq(dl_se))
 		return;
@@ -1236,23 +1235,13 @@  static void update_curr_dl(struct rq *rq)
 	 * natural solution, but the full ramifications of this
 	 * approach need further study.
 	 */
-	now = rq_clock_task(rq);
-	delta_exec = now - curr->se.exec_start;
-	if (unlikely((s64)delta_exec <= 0)) {
+	delta_exec = update_curr_common(rq);
+	if (unlikely(delta_exec <= 0)) {
 		if (unlikely(dl_se->dl_yielded))
 			goto throttle;
 		return;
 	}
 
-	schedstat_set(curr->se.statistics.exec_max,
-		      max(curr->se.statistics.exec_max, delta_exec));
-
-	curr->se.sum_exec_runtime += delta_exec;
-	account_group_exec_runtime(curr, delta_exec);
-
-	curr->se.exec_start = now;
-	cgroup_account_cputime(curr, delta_exec);
-
 	if (dl_entity_is_special(dl_se))
 		return;
 
diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
index 2ba8f230feb9a..10a230d85104a 100644
--- a/kernel/sched/fair.c
+++ b/kernel/sched/fair.c
@@ -836,30 +836,58 @@  static void update_tg_load_avg(struct cfs_rq *cfs_rq, int force)
 }
 #endif /* CONFIG_SMP */
 
+static s64 update_curr_se(struct rq *rq, struct sched_entity *curr)
+{
+	u64 now = rq_clock_task(rq);
+	s64 delta_exec;
+
+	delta_exec = now - curr->exec_start;
+	if (unlikely(delta_exec <= 0))
+		return delta_exec;
+
+	curr->exec_start = now;
+	curr->sum_exec_runtime += delta_exec;
+
+	schedstat_set(curr->statistics.exec_max,
+		      max(delta_exec, curr->statistics.exec_max));
+
+	return delta_exec;
+}
+
+/*
+ * Used by other classes to account runtime.
+ */
+s64 update_curr_common(struct rq *rq)
+{
+	struct task_struct *curr = rq->curr;
+	s64 delta_exec;
+
+	delta_exec = update_curr_se(rq, &curr->se);
+	if (unlikely(delta_exec <= 0))
+		return delta_exec;
+
+	account_group_exec_runtime(curr, delta_exec);
+	cgroup_account_cputime(curr, delta_exec);
+
+	return delta_exec;
+}
+
 /*
  * Update the current task's runtime statistics.
  */
 static void update_curr(struct cfs_rq *cfs_rq)
 {
 	struct sched_entity *curr = cfs_rq->curr;
-	u64 now = rq_clock_task(rq_of(cfs_rq));
-	u64 delta_exec;
+	s64 delta_exec;
 
 	if (unlikely(!curr))
 		return;
 
-	delta_exec = now - curr->exec_start;
-	if (unlikely((s64)delta_exec <= 0))
+	delta_exec = update_curr_se(rq_of(cfs_rq), curr);
+	if (unlikely(delta_exec <= 0))
 		return;
 
-	curr->exec_start = now;
-
-	schedstat_set(curr->statistics.exec_max,
-		      max(delta_exec, curr->statistics.exec_max));
-
-	curr->sum_exec_runtime += delta_exec;
 	schedstat_add(cfs_rq->exec_clock, delta_exec);
-
 	curr->vruntime += calc_delta_fair(delta_exec, curr);
 	update_min_vruntime(cfs_rq);
 
diff --git a/kernel/sched/rt.c b/kernel/sched/rt.c
index f215eea6a9661..196171fbf5978 100644
--- a/kernel/sched/rt.c
+++ b/kernel/sched/rt.c
@@ -997,26 +997,15 @@  static void update_curr_rt(struct rq *rq)
 {
 	struct task_struct *curr = rq->curr;
 	struct sched_rt_entity *rt_se = &curr->rt;
-	u64 delta_exec;
-	u64 now;
+	s64 delta_exec;
 
 	if (curr->sched_class != &rt_sched_class)
 		return;
 
-	now = rq_clock_task(rq);
-	delta_exec = now - curr->se.exec_start;
-	if (unlikely((s64)delta_exec <= 0))
+	delta_exec = update_curr_common(rq);
+	if (unlikely(delta_exec < 0))
 		return;
 
-	schedstat_set(curr->se.statistics.exec_max,
-		      max(curr->se.statistics.exec_max, delta_exec));
-
-	curr->se.sum_exec_runtime += delta_exec;
-	account_group_exec_runtime(curr, delta_exec);
-
-	curr->se.exec_start = now;
-	cgroup_account_cputime(curr, delta_exec);
-
 	if (!rt_bandwidth_enabled())
 		return;
 
diff --git a/kernel/sched/sched.h b/kernel/sched/sched.h
index 3fd283892761d..963c16fc27500 100644
--- a/kernel/sched/sched.h
+++ b/kernel/sched/sched.h
@@ -1769,6 +1769,8 @@  extern const u32		sched_prio_to_wmult[40];
 
 #define RETRY_TASK		((void *)-1UL)
 
+extern s64 update_curr_common(struct rq *rq);
+
 struct sched_class {
 
 #ifdef CONFIG_UCLAMP_TASK
diff --git a/kernel/sched/stop_task.c b/kernel/sched/stop_task.c
index 394bc8126a1e5..1eb1e336e18e7 100644
--- a/kernel/sched/stop_task.c
+++ b/kernel/sched/stop_task.c
@@ -62,21 +62,7 @@  static void yield_task_stop(struct rq *rq)
 
 static void put_prev_task_stop(struct rq *rq, struct task_struct *prev)
 {
-	struct task_struct *curr = rq->curr;
-	u64 delta_exec;
-
-	delta_exec = rq_clock_task(rq) - curr->se.exec_start;
-	if (unlikely((s64)delta_exec < 0))
-		delta_exec = 0;
-
-	schedstat_set(curr->se.statistics.exec_max,
-			max(curr->se.statistics.exec_max, delta_exec));
-
-	curr->se.sum_exec_runtime += delta_exec;
-	account_group_exec_runtime(curr, delta_exec);
-
-	curr->se.exec_start = rq_clock_task(rq);
-	cgroup_account_cputime(curr, delta_exec);
+	update_curr_common(rq);
 }
 
 /*